SECONDARY PRODUCTION WITHIN A SEAGRASS BED (ZOSTERA-MARINA AND RUPPIA-MARITIMA) IN LOWER CHESAPEAKE BAY

Monthly sampling of a 140-ha seagrass bed in the lower Chesapeake Bay, Virginia, revealed that 13 numerically and trophically important species, representing about 20% of the total community densities over the year-long study period, accounted for the production of approximately 42 g dry wt m-2 yr-1. This estimate is likely conservative due to our assumptions on voltinism and fixed size at maturity regardless of season for the species studied. The isopod Erichsonella attenuata accounted for 17.6 g dry wt m-2 yr-1 or 42% of the calculated total production, while the portunid decapod Callinectes sapidus and the amphipod Gammarus mucronatus each accounted for 7.7 g dry wt m-2 yr-1. The 10 remaining species (4 peracarids, 4 molluscs, and 2 decapods) each produced less than 2 g dry wt m-2 yr-1. Total seagrass-associated secondary production was estimated to equal or exceed 200 g dry wt m-2 yr-1. By applying this estimate to the entire 140-ha grassbed, we projected that, on average, 4.8 metric tons dry wt of invertebrate standing stock and 55.9 metric tons of invertebrate production occur over the year.